The invention relates to a hydraulic drive for slides of a multiple-slide forging machines as known from DE-C2 38 03 632.
The slides of such a forging machine, each bearing a tool, are built as pistons which, at their end opposite to the tool acted upon by a pressure medium, are provided with a valve seat connected to a central throughflow bore, which via side channels is connected to a chamber kept pressureless by means of a discharge line. A valve lifter controlled by an actuator cooperates with the valve seat on the piston and controls the piston stroke. The pistons are designed as differential pistons and are constantly acted upon by the pressure medium at their piston ring surface in the pull-back direction. This drive system is characterized by its good dynamics and simple construction.
Because of its good dynamics, this drive system is well suited for use in high-speed forging presses, which as a replacement of forging hammers, should reach 180 to 240 strokes per minute. The problem here is that forging presses have to be laid out for substantially bigger strokes than the relatively short-stroke forging machines, whereby the axial length of the drive system and the slide mass increase correspondingly.
It is the object of the invention to improve the drive system known from DE-C2 38 03 632 rendering it applicable to high-speed forging presses.
In order to solve this problem a reduction of the axial length of the drive system with the reduction of its mass is targeted, which is achieved by making the piston partially hollow starting from its end opposed to the tool. On the bottom of the hollow is the valve seat. The valve lifter is tubular in shape and guided so as to be axially displaceable in the cylinder lid and is provided with side channels in the cylinder lid connecting the inner space of the valve lifter with a chamber surrounding the valve lifter kept without pressure via a discharge line.
In order to achieve this object of the invention aimed at the reduction of the axial length of the drive system, according to another feature of the invention, it is further developed in an embodiment in which the differential piston step is eliminated.
The piston is built as a plunger piston which at its tool end is connected with a tool-bearing upper plate/front plate, which by means of guide rods is guided in the traverse. The return stroke of the plunger piston is performed by means of the piston-cylinder units supported in the traverse.
Four guide rods are preferably provided which are connected in pairs above the traverse by yoke pieces and between the same and the traverse the piston-cylinder units are arranged for the pull-back.
During the forging operations the pull-back pistons are constantly acted upon from an accumulator to keep them inactive.